Life support for astronauts includes the treatment and revitalization of the air that the astronauts breathe. Part of the revitalization is the removal of the excess water vapor from the air. This excess water vapor is a result of the natural metabolic production of water, and it is exhausted into the air by the astronaut's respiration and perspiration. The condensation of water in zero gravity and its separation from the remaining gaseous phase while in a zero gravity environment is technically challenging and requires a solution. In addition to the condensing and gas/liquid separation problem, there is the problem of biological fouling of the condensing/separation mechanism, being employed as part of the life support system, due to deposition and subsequent growth by microorganisms on the condensing surface of the condensing/separation mechanism. Not only does this fouling potentially reduce the effectiveness of the condenser/separator, but also represents a contamination point for the astronauts' water system.
The problem of condensing the water vapor from humidity laden air in a zero gravity environment is very similar to the problem of removing the liquid water from a two-phase fuel cell gas circulation stream. Several solutions to the fuel cell problem have been implemented and include: centrifugal separators, porous media, and membrane separators.
Centrifugal separators (both rotating and non-rotating) operate by imparting an acceleration to water droplets, and since the water drops are denser than the surrounding gas, they are “spun” separated from the gas being treated by the centrifugal separators. If the centrifugal separators are rotating, they consume power, if non-rotating their operation is flow rate dependent. The centrifugal separators are also most susceptible to dry-out conditions. However, the centrifugal separators are the least susceptible, compared to the porous media and membrane support, to fouling or plugging because the treated water does not get squeezed through tiny pathways found in porous media and membrane support devices. Scaling, that is adapting the centrifugal separators to different applications, is the most difficult of the three different type solutions.
Porous media (sintered metal, plastic or ceramic particles) operate by absorbing the condensate on a surface of interest, and by a combination of capillary forces and bulk pressure differential to transfer of water from a higher pressure gas/liquid side to a lower pressure liquid only side. The materials (sintered metal, plastic or ceramic particles) must be either inherently hydrophilic or treated to make them hydrophilic in order for a required absorption process to work. These porous media separators are considerably thicker than membrane separators, and therefore are far more resistant to water flow. This means that these separators must be sized larger, or have a greater delta P, known in the art, for driving the water through the separators than that required for membrane technique. However, the porous media technique scales easily, but unfortunately is susceptible to fouling. Furthermore, the porous media devices are generally much heavier than typical membranes, but are easily shaped into different geometries (cylindrical, planar, etc.).
Membrane separators (hydrophobic, hydrophilic, or both in combination) are very similar to the porous technique employing porous media for removing water from a two-phase fuel cell gas, but are far less flow restrictive, and therefore can be made much smaller/lighter for a given water removal rate. The membrane separator can be made to operate with low delta P. The membrane separators also scale easily, but also foul just as easily as porous media. Advantageously, the membrane separators can be made into pleated cylindrical or planar geometries. The hydrophobic type of the membrane separators operate by allowing gas to flow through the hydrophobic membrane, but not liquid. Conversely, the hydrophilic type of membrane separators allow liquid to pass, but not gas. These hydrophilic membranes are typically plastic, but sometimes are thin deposited layers of either metals, plastics or ceramics on a thicker supporting substrate. It is desired to incorporate the beneficial features of the hydrophilic membrane and centrifugal separators into a system that corrects for the problem of condensing water vapor from humidity laden air in a zero gravity environment. It is further desired to provide a system that provides purifying, condensing, filtering and humidifying functions for the Zero-G life support system for astronauts, as well as for home and office building air conditioning apparatuses, airplane air systems, automobile air systems, room humidifiers and room air cleaners.